THE ANIMAL IN THE WORLD 547 



stated is indisputable. Over their explanation, however, 



rages the great controversy of Biology. The 

 and^tauTm. mechanistic school of biologists regards all 



the phenomena of life as due to the laws of 

 physics and chemistry, and looks forward to the day when 

 the extension of our knowledge will enable us to explain 

 them all in terms of these sciences. The apparent ex- 

 ceptions to the laws of chemistry and physics are, for it, 

 not real exceptions, but are due only to our ignorance 

 of the details of the processes in which they occur. The 

 purposive direction of the life processes is due to the 

 structure of the living machine, though here again our 

 ignorance does not allow us to see how it is brought about. 

 The vitalistic school believes that the present impossibility 

 of understanding biological phenomena in the light of 

 physical and chemical facts is due to the operation in 

 living beings of a further factor or factors, without a know- 

 ledge of which life will never be explained. It is held that 

 no machine can be conceived which would direct its own 

 activity in the way in which the' activity of a living being 

 is directed — that, indeed, the word " machine " can only be 

 used in a limited sense of a living organism. As to the 

 nature of the factor in question, if it exist, nothing is known, 

 though there is a tendency among vitalists to regard it as 

 psychical, but it must in any case be able to direct the 

 physical and chemical forces of life without increasing or 

 diminishing their energy. 



The problem of the peculiarities of life is bound up 



with that of its origin. If we understood 

 The Origin of how life arose we should know to what its 

 ised'Bodfes!" peculiarities are due, though it is true that we 



might well know this without being able to 

 reproduce it. Life, as we have seen, is found only in 

 organised bodies, though not all organised bodies are alive. 

 We may class material objects as follows : — 



Organised {^f 

 Unorganised 



\ Lifeless. 



It is possible that if we knew how organised bodies first 

 arose we might understand the origin of life, but this is by 



36 



